1. Field of the Invention
The present invention relates to a mobile IP service and, more particularly, to a mobile IP service method of a mobile node after hand-off.
2. Background of the Background Art
Recently, as use of the mobile communication and wireless local area network (LAN) spread widely, the Internet service centered upon fixed terminals, depending on a wide area network (WAN) or a LAN, has dwindled while internet access using a mobile terminal has increased. In addition, research on mobile terminal internet access is being actively conducted. Accordingly, methods allowing an ATM network or a mobile communication network to accommodate an Internet protocol (IP) have been proposed by an Internet engineering task force (IETF) and an ATM forum, and a standardization is being made.
Currently, an IP version 4, mostly used in the Internet environment, is based on the assumption that in order for a node to receive a datagram transmitted to itself, the node is to be located within a network having an IP address of the node. If the node's location is changed, the datagram is not to be transmitted.
To support mobility of the node in the Internet, a more extensive technique is required, for which an IETF is currently promoting an RFC2002 as a standardization plan. The recommended standard (RFC2002) proposes a technical method allowing an existing IP address for a mobile node (MN) to be used without change, even though the MN connected to a TCP/IP network is moved to a different area.
FIG. 1 is a drawing illustrating a concept of a mobile IP service on the basis of the recommended standard (RFC2002). As an IP host having mobility, the mobile node transmits and receives data using a home IP address. When the MN 11 visits visiting networks 12 and 12′, the foreign agents (FA) 13 and 13′ de-capsulate an IP packet bound for the MN 11 and transmit the IP packet, while having a link connection with the MN 11. A home agent (HA) 15 is positioned at a pertinent home network 14 of the MN 11. The HA 15 manages a binding table of the MN 11, encapsulation of the IP packet bound for the MN 11, and transmits the IP packet.
FIG. 4 is a drawing illustrating a background art registration procedure of the hand-off MN. Processes performed to continuously support the mobile IP service to the hand-off MN 11 can be divided into three steps, which will now be described.
First, a step for finding an agent is performed (step S1). The mobility agent, such as the HA 15 or the FAs 13 and 13′, broadcast an agent advertisement message to its own network areas 12 and 12′ and, upon receiving the agent advertisement, the MN 11 determines the identity of the network area in which it is located. That is, if a new advertisement message, different to a previous advertisement message, is transmitted at an arbitrary time point to the MN 11, it signifies that the MN 11 was moved away from the area (network 1) of the previous FA 13 and has been moved into an area (network 2) of a different FA 13′. The agent advertisement message is a kind of area indication message that the agent 13, 13′ and 15 transmits to its own network area, and the MN 11 recognizes the area where it is located through the agent advertisement.
Second, a registering step is performed. According to the agent finding step, if the MN 11 has been moved into a different network 12′ area, the MN 11 and the HA 15 exchange a registration request message and a registration reply message, through which the MN 11 is registered in the MN 11. The registration messages are transmitted through a user datagram protocol (JDP) port and includes a care-of-address (COA) life time of the MN 11. The COA signifies an agent address of a network where the MN 11 is located.
Third, a routing and tunneling step is performed. As the MN 11 is successfully registered in the HA 15, a datagram transmitted from an external source to the MN 11 is tunneled to the COA, of the MN 11, by the HA 15. If an address of the FA is designated in the COA, the FA performs a de-capsulating. If the address of the FA is used as a co-located COA, the datagram to the MN 11 is de-capsulated, also.
The tunnel (or the IP tunnel) is a communication path used by the encapsulated datagram. HA 15 is a starting point of the tunnel and performs encapsulating, and the node for de-capsulating is the end point of the tunnel. The de-capsulating node is an object for transmitting the de-capsulated datagram to a destination, as well as de-capsulating the datagram.
If an address of the FA is designated in the COA, the FAs 13 and 13′ operate as a de-capsulating node, but if the address of the FA is used as a Co-Located COA, the MN 11 operates as a de-capsulating node.
The process of the registering step is described below. First, MN 11 transmits a registration request message to the agent 13′ of the network 12′ in which the MN 11 is located. Second, the agent 13′, that is, the FA 13′, performs a predetermined registration procedure and transmits the registration request message to the HA 15. Third, the HA 15 transmits a registration allowance reply message or a registration refusal reply message to the FA 13′, in response to the registration request. And fourth, the FA 13′ transmits the received registration reply message to the MN 11.
The registering step will now be described in greater detail with reference to FIGS. 1 and 4. The MN 11 is moved (handed-off) from a service area (network 1) of a previous FA (referred to as ‘old FA’, hereinafter) to a service area (network 2) of a new FA 13′ (step S0). Then, the MN 11 transmits a registration request message (type=‘1’) to the agent 13′ of the currently located network 12′ (step S2). Upon receiving the registration request message, the FA 13′ registers the MN 11 in a visitor table and transmits the registration request message to the HA 15 (steps S3-S5).
If the FA 13′ does not allow the registration of the MN 11, the FA 13′ transmits a registration reply message, having a predetermined registration disallowance code (64˜73 or 80˜82 or 88) in a code field, to the MN 11, rather than transmitting the MN's 11 registration request message to the HA 15 (steps S3 and S6). If the registration request of the MN 11 is allowed by the FA 13′ but is not allowed by (steps S3-S5 and S7-S9) the HA 15, the FA 13′ deletes the registration of the MN 11 stored in the visitor table.
When the HA 15 receives the registration request message of the MN 11, the HA 15 updates the binding table, with reference to an address value stored in the COA field of the registration request message (step S10). In this respect, as a matter of course, the HA 15 performs such operations only when there is no error in the registration request. After the binding table is updated, HA 15 communicates a registrated allowance message to the MN 11, via FA 13′ (steps S12 and S13).
If the HA 15 disallows the registration of the MN 11, the HA 15 transmits the registration reply message, having the predetermined registration disallowance codes (128˜136) in the code field, by way of the FA 13′ (step S11). If the MN 11 is successfully registered in the FA 13′ and the HA 15, an IP tunnel is established between the FA 13′ and the HA 15. And, the HA 15 transmits the IP datagram, received from an Internet host, to the MN 11 through the established IP tunnel. At this time, the ending point of the IP tunnel is the FA 13′ and the address of the FA 13′ is called the care-of-address (COA).
Before transmitting the IP datagram to the IP tunnel, the HA 15 encapsulates the IP datagram to generate an IP packet. And, the FA 13′ de-capsulates the IP packet, received through the IP tunnel, and transmits it to the MN 11.
The registration of the MN 11, stored in the visitor table of the FA 13′, is effective only for the life time set in the registration request message. If re-registration is not made until the life time is terminated, the mobile binding table of the HA 15 and the registration of the MN 11, stored in the visitor table of the FA 13′, are deleted, so that the MN 11 may not be provided with the mobile IP service any longer.
Since the IP packet from the Internet host is routed to the MN 11, through the above process, the MN 11 is provided with the mobile IP service even after its position is changed to a different service area. In addition, the MN 11 can continuously use its own home IP address, which has already been set, as the mobile IP address, regardless of the service area in which it is currently located.
FIG. 2 is a drawing illustrating an example of a registration request message and a registration reply message. Each field and set-up value of the registration request message and the registration reply message, illustrated in FIG. 2, will now be described.
If the set-up value of a field ‘type’ of a message is ‘1’, it is a registration request message, while if the set-up value of the field ‘type’ is ‘3’, it is a registration reply message. The ‘S’ field of the registration request message indicates a simultaneous binding. If the ‘S’ bit is set to (‘1’), HA 15 maintains a previous mobility binding of the MN 11, as it is. Field ‘B’ is a broadcast datagram. If indicator bit ‘B’ has been set, HA 15 transmits the broadcast datagram received by the home network to the MN 11.
Field ‘D’ is de-capsulation indicator. If the bit ‘D’ has been set, it signifies that the MN 11 de-capsulates the datagram. That is, the co-located FA 13′ is used as a mobile IP address of the MN 11.
When using the COA, the MN 11 registered for the FA 13′ receives data by relying on the address of the FA 13′. The co-located FA 13′ is used when the MN 11 has a local address connected to a network interface.
Field ‘M’ is a minimum encapsulation indicator. If bit ‘M’ is set, HA 15 encapsulates data transmitted to MN 11, minimally. Field ‘G’ is a ‘GRE’ encapsulation indicator. If bit ‘G’ is set, HA 15 GRE-encapsulates a datagram, to be transmitted to MN 11, and transmits it. If bit ‘V’ is set, the mobility agent 13,13′ and 15 transmits data using a VanJacobson header compression method on a link connected to the MN 11. The ‘rsv’ field is reserved and its bits are set to ‘0’. In the life time field, a predetermined time is set and registration of the MN 11 is effective for the predetermined time.
The home address is an IP address of the MN 11. The home agent is an IP address of the HA 15. The COA is an IP address of the ending point of the tunnel. The identification field is 64-bit number constructed by the MN 11 to associate the registration request and the registration reply.
The code field of the registration reply message indicates a result of the registration request. That is, the HA 15 or the new FA 13′ set the result (registration permission or registration disallowance) of the registration request of MN 11. A code value of ‘0’ or ‘1’ signifies a registration permission and a code value of ‘64˜73’, ‘80˜82’ or ‘88’ signifies a registration disallowance, by the FA. If the code value is 128˜136′, it signifies a registration disallowance by the HA 15.
The meaning of the home address field and home agent field values are the same as for registration request message. A value for the identification field is a 64-bit number, set on the basis of the identification field of the MN's 11 registration request message and is used to match the registration request with a particular registration reply. Additionally, it is used to prevent a reply denial to the registration message. Thus, upon receiving the registration request message of the MN 11, the HA 15 creates or corrects a binding table for the MN 11, with reference to a set value of each field and bit contained in the registration request message.
As noted, even though the location of the MN 11 is changed, the FA 13 is not informed of the hand-off of the MN 11, by the HA 15 or the MN. Thus, the FA 13 retains the visitor table until the set life time is terminated, causing waste of the memory.
Referring now to the mobile communication network shown in FIG. 3, when a mobile station (MS) 105 is moved into an area of the PSDN 102′, while still receiving a service in the service area of a packet data serving node (PSDN) 102, the PDSN 102 still occupies the visitor table of the MS 105. A radio link resource of MS 105 and BS 103 manages the information of the MS 105, which does not exist in its own service area since it has been handed off. This results in the waste of PDSN 102 and BS 103 resources.
The BSs 103 and 103′ are objects incorporating a base station transceiver, a base station controller, and a packet controller function. The three objects are all independent mobile communication equipment. The equipment is simply represented by the BSs 103 and 103′ for the sake of brevity.
As another example, suppose that the MS 105, which has been handed off to a service area of PDSN 102′, is handed off back to the service area of PDSN 102 before its own life time registered in PDSN 102 is terminated. MS 105 has been registered in the binding table of PDSN 102 and the set time of the life timer is still effective. Therefore, even though MS 105 transmits a registration request message, PDSN 102 and BS 103 refuse to receive the registration request. Thus, when the set time of the life timer is terminated, a dead lock registration takes place. Even though MS 105 is actually located in the service area of BS 103, BS 103 does not recognize it MS 105 since BS 103′ recognizes MS 105 as being located in the service area of BS 103′.
In order to solve the dead lock registration problem and the waste of memory resources, various methods and algorithms have been proposed. However, each of these disadvantageously requires additional resources to solve the problems.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.